Originally Posted by Freakscene
This is annoying. There are methods to polish elements to avoid this, but lens manufacturers typically don't employ them.
This is from a 35 Summilux ASPH (the pre-FLE one). Annoying, it looks weird.
that looks a bit like cavity resonance to me a la Fabry-Perot, like a surface pair is locally close to plane parallel. If so that might be unavoidable with the geometry in question. (I say this in part because the image looks near-monochromatic: does it still do it with white, with no colour fringing "in the onion rings"?).
If you mean the method of "machining" aspheric surfaces with a diamond stylus and then not smoothing the grooves, I guess this is one way to avoid too much cost increase: if you look at optic catalogues and the same-size, same-glass, same-EFL, same-surface tolerance precision asphere is 2-5x the price of the corresponding spherical item that input cost has to either be passed on to the consumer or reduced somehow. I guess it boils down to microfacets left on glass or moulded plastic (at least index matched caps) or less money spent elsewhere (or price hike).
Originally Posted by jarski
Now, what is APO then, in layman's terms?
I see what you did there
To be fair though I don't think you could really get away with designing a lens with, say violet, red and like 740nm or so (which might be reliably picked up by most IR films) brought to the same focus but a huge excursion peaking at 500nm, call it APO and rake in the dollars. But yeah, the similarity in terms of marketing the method rather than the results is... uh... hard to overlook
Once again: I'm not talking about specific lenses which are or are not marketed as ASPH, APO or anything. I'm not insulting your decision to use, or not use any lens so marketed or opinions of same. I'm talking about what, if anything, that marketing implies to you as a consumer. Most of the responses so far have been useful, illustrative and/or entertaining.